Display device, driving method of display device, and electronic apparatus

Abstract

A display device includes a pixel electrode and a counter electrode facing each other, a plurality of charged particles disposed between the pixel electrode and the counter electrode, an organic transistor electrically connected to the pixel electrode, a data line electrically connected to the pixel electrode via the organic transistor, a data line driving circuit supplying an image signal to the data line, and a counter electrode driving circuit supplying a counter electrode driving signal containing a pulse signal having the same polarity as the image signal to the counter electrode.

Description

BACKGROUND[0001]1. Technical Field[0002]The present invention relates to a display device including an organic transistor, a driving method of a display device, and an electronic apparatus.[0003]2. Related Art[0004]Organic semiconductors are promising future semiconductors succeeding silicon and compound semiconductors and their wide application to various electronic apparatuses are expected. In particular, development of the organic semiconductors has led to realization of thin, light and flexible devices which can be freely bent and also to realization of production of electronic price label (information tag) that can enable individual products to be managed in wireless, so research and development on practical use of the organic semiconductors are progressing. For example, a flexible display represented by electronic paper can serve as an electronic apparatus which bears a part of ubiquitous society thanks to its advantages of the ability of shock absorption and the pliability wh...

AI Technical Summary

Benefits of technology

[0011]In the display device, it is preferable that the pulse width of the pulse signal differs from an interval between pulses of the pulse signal. As mentioned above, the pulse signal supplied to the counter electrode and a signal attributable to the off-current supplied to the pixel electrode are offset and thus the force in a direction opposite to a direction in which the charged particles may move in the pixels whose organic transistors are in an ON state is applied to the charged particles in the pixels whose organic transistors are in an OFF state. Accordingly, the pulse signal with a larger pulse width is effective in suppressing undesirable movement of the charged particles. On the other hand, the pulse signal supplied to the counter electrode and the image signal supplied to the pixel electrode are offset with respect to the pixels whose organic transistors are in an OFF state. Accordingly, it is effective to extend the interval between pulses, the period in which the pulse signal is not supplied, in improving write speed of an image in such pixels. As described above, whichever the pulse width of the pulse signal and the interval between the pulses of the pulse signal is set too large, such setting is unsuitable as a display, and it is necessary to set up the amplitude of the pulse signal and the interval between the pulses suitably according to desired level of contrast and the write speed of an image.

[0012]For example, in cases in which the organic transistor is a P-channel transistor, in the pixel which performs write operation (whose organic transistor is in an ON state), a gate bias of the organic transistor is defined by a potential difference between a ground potential and a potential applied to a source thereof. Accordingly, it is possible to control the gate bias at a predetermined level. On the other hand, in the pixel which does not perform write operation (whose organic transistor is in an OFF state), since the gate bias of the organic transistor is defined by a potential difference between a ground potential and a potential attributable to charges accumulated in the pixel electrode, the gate bias changes according to the charges accumulated in the pixel electrode. For this reason, the average of the gate biases of the organic transistors of the pixels which do not perform write operation is relatively small, and thus it is possible to adjust the pulse width of the pulse signal so as to be larger than the interval between the pulses of the pulse signal, according to the decreased gate bias. Such situation is also applied to the case in which the organic transistor is an N-channel transistor. Even as for the N-channel organic transistor, it is preferable that the pulse width of the pulse signal is larger than the interval between pulses of the pulse signal, which can lead to provision of a display device having excellent display quality.

[0013]In the display device, it is preferable that the display device further includes a scan line electrically connected with the pixel electrode via the organic transistor and a scan line driving circuit which supplies a scan signal to the scan line, in which the counter electrode driving circuit supplies one pulse or at least two pulses to the counter electrode during a period in which one scan signal is supplied. Thanks to such a structure, it is possible to decrease moving distance by which the charged particles move due to the off current of the organic transistor, which can lead to provision of a display device having high contrast.

[0014]In the display device, it is preferable that the scan line driving circuit performs scan operation with respect to the scan line a plurality of times within a period of one frame. Thanks to such a structure, it is possible to decrease scan time for each scan operation. Accordingly, it becomes possible to decrease influence of the charge trap which was a problem in the field of the organic transistors. That is, as for the organic transistors, it is known that a phenomenon called charge trap that current which flows through a transistor decreases as time passes due to migration of opposite charges from a gate electrode to a channel region exists. Since the opposite charges generated by the charge trap is reduced as time passes, it is possible to suppress influence of the charge trap to the minimum by decreasing the scan time for each scan operation and thereby increasing the number of times of scan operations with respect to the scan line.

[0015]According to another aspect of the invention, there is provided a driving method of a display device in which a plurality of charged particles is disposed between a pixel electrode and a counter electrode and an image is displayed by moving the charged particles by electric field formed between the pixel electrode and the counter electrode, the driving method including supplying a pulse signal having the same polarity as an image signal to the counter electrode upon supplying the image signal to the pixel electrode via an organic transistor and making the charged particles move in a direction opposite to a direction in which the charged particles move in response to the image signal with respect to pixel electrodes in pixels other than pixels whose organic transistors are in an ON state. With the driving method, the pulse signal having the same polarity as the image signal is supplied to the counter electrode. Accordingly, even if the off current flows through the organic transistor, it is possible to draw the charged particles in a direction opposite to a direction in which the charged particles would move due to the off current. For this reason, although the charged particles move to a position which is different to a position where the charged particles must exist essentially by the off current of the organic transistor, it is possible to detain the charged particles in the position where the charged particles must exist essentially by the influence of the pulse signal. In this case, movement of the charged particles is suppressed in the pixels whose organic transistors are in an ON state. However, the charged particles can continuously move in the display device using the charged particles as long as the electric field is formed by the charges accumulated in the pixel electrode. For this reason, even if supply of the image signal is temporarily suspended by the pulse signal, there is no likelihood that movement of the charged particles is perfectly inhibited. According to this aspect, it is possible to prevent the charged particles from undesirably moving to the pixel electrode in association with the organic transistor which is in an OFF state and thus it is possible to provide a display device having excellent display quality.

[0016]According to a further aspect of the invention, there is provided an electronic apparatus including the display device according to the above-mentioned aspect. According to this aspect, since the electronic apparatus employs the organic transistor as a pixel switching element, the electronic apparatus can be realized by using a flexible substrate such as plastic substrate. As a result, an electronic apparatus having excellent display quality can be realized.

Problems solved by technology

That is, under the present circumstances, the performance necessary for a switching element is not obtained by the organic transistor.

For this reason, when the number of scanning lines is increased, it happens that a voltage, which originally must not be applied, is applied to a pixel electrode due to the off-current (leak current in an OFF state) of an organic transistor, leading to deterioration of contrast and occurrence of cross talk.

However, in the display device using the charged particles, although the image signal is not continuously supplied, the charged particles can continuously move as long as electric field is formed by charges accumulated in the pixel electrode.

Accordingly, even if supply of the image signal is temporarily suspended by the pulse signal, the movement of the charged particles may not be perfectly inhibited.

As described above, whichever the pulse width of the pulse signal and the interval between the pulses of the pulse signal is set too large, such setting is unsuitable as a display, and it is necessary to set up the amplitude of the pulse signal and the interval between the pulses suitably according to desired level of contrast and the write speed of an image.

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